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A reply to a discussion by Chandra and Aimin of the paper “assessment of simple methods of determining the free chloride ion content of cement paste”
CEMENT and CONCRETE RESEARCH. Vol. 18, pp. 664-665, 1988. Printed {n the USA. 0008-8846/88 $3.00+00. Copyright (c) 1988 Pergamon Press plc
A REPLY "Assessment
to a D i s c u s s i o n by C h a n d r a and A i m i n of the p a p e r of S i m p l e M e t h o d s of D e t e r m i n i n g the Free C h l o r i d e Ion C o n t e n t of C e m e n t Paste".
C. Arya,
N.R. B u e n f e l d and J.B. N e w m a n Concrete Section D e p a r t m e n t of c i v i l E n g i n e e r i n g I m p e r i a l C o l l e g e of S c i e n c e and T e c h n o l o g y London, SW7 2BU.
we t h a n k
S.
Chandra
and Xu A i m i n
for t h e i r
contribution.
We a g r e e t h a t the c h e m i c a l and p h y s i c a l reactions w h i c h take place between chloride ions and cement minerals are rather d i f f e r e n t d e p e n d i n g u p o n w h e t h e r the c h l o r i d e ions are admixed, or e x t e r n a l l y d e r i v e d . We i n v e s t i g a t e d the m o r e s i m p l e c a s e of admixed chloride first to a v o i d the complication of c h l o r i d e gradients which would have made interpretation of pore press results difficult. A s e c o n d s e r i e s of t e s t s now c o m p l e t e d show that leaching techniques can be used to determine the free chloride ion c o n t e n t of s p e c i m e n s c o n t a i n i n g e x t e r n a l l y d e r i v e d chloride, but that less severe extraction conditions are necessary. It is o u r e x p e r i e n c e t h a t a f t e r g r i n d i n g , c e m e n t p a s t e of any age will continue to h y d r a t e if i m m e r s e d in water. For the m i x e s t e s t e d the c h a n g e s in pore s o l u t i o n c o m p o s i t i o n w e r e s u f f i c i e n t l y small b e y o n d 28 d a y s for us to a c c e p t t h i s as a r e a s o n a b l e p e r i o d of curing. The aim of the work on p a r t i c l e size was to d e t e r m i n e the i n f l u e n c e of f i n e n e s s on the q u a n t i t y of c h l o r i d e p a s s i n g into solution for a practical period of leaching. The effect of l e a c h i n g t i m e was s t u d i e d s e p a r a t e l y (see f i g u r e s 4-6). E t h a n o l was i n c l u d e d as an a l t e r n a t i v e s o l v e n t to w a t e r in our s t u d y b e c a u s e o t h e r w o r k e r s [1,2] had p r e v i o u s l y a s s u m e d that the c h l o r i d e s l e a c h e d into e t h a n o l g i v e a g o o d a p p r o x i m a t i o n of the free chloride ion content; in one case, drawing important c o n c l u s i o n s r e g a r d i n g the s t a t e of c h l o r i d e in c o n c r e t e b a s e d on this assumption. Our theoretical work suggested that this a s s u m p t i o n c o u l d well be i n c o r r e c t and we felt it w o r t h w h i l e to investigate this experimentally. We have not studied the chemical c o n s t i t u e n t s of h a r d e n e d c e m e n t p a s t e 664
interaction and m e t h a n o l
between and, in
the view
Vol. 18, No. 4
665 OISCUSSIONS
of the p o o r p e r f o r m a n c e of m e t h a n o l as a l e a c h i n g agent, it is not our i n t e n t i o n to do so. H o w e v e r , our u n d e r s t a n d i n g of the l i t e r a t u r e [3] is t h a t it is by no m e a n s an e s t a b l i s h e d fact that methanol reacts with cement paste constituents. References i. V.S. R a m a c h a n d r a n , M a t e r i a u x et Constr., 14, 3 (1971). 2. N. Tenoutasse, "A simple method for the determination of calcium chloride during cement hydration", International Symposium on A d m i x t u r e s in m o r t a r s and c o n c r e t e , Brussels, R I L E M - A B E M , R e p o r t V / 1 5 V, 261 (1967). 3. L.J. Parrot, Cem. Concr. Res., 13, 65 (1983).
A REPLY "Assessment
to a D i s c u s s i o n by C h a n d r a and A i m i n of the p a p e r of S i m p l e M e t h o d s of D e t e r m i n i n g the Free C h l o r i d e Ion C o n t e n t of C e m e n t Paste".
C. Arya,
N.R. B u e n f e l d and J.B. N e w m a n Concrete Section D e p a r t m e n t of c i v i l E n g i n e e r i n g I m p e r i a l C o l l e g e of S c i e n c e and T e c h n o l o g y London, SW7 2BU.
we t h a n k
S.
Chandra
and Xu A i m i n
for t h e i r
contribution.
We a g r e e t h a t the c h e m i c a l and p h y s i c a l reactions w h i c h take place between chloride ions and cement minerals are rather d i f f e r e n t d e p e n d i n g u p o n w h e t h e r the c h l o r i d e ions are admixed, or e x t e r n a l l y d e r i v e d . We i n v e s t i g a t e d the m o r e s i m p l e c a s e of admixed chloride first to a v o i d the complication of c h l o r i d e gradients which would have made interpretation of pore press results difficult. A s e c o n d s e r i e s of t e s t s now c o m p l e t e d show that leaching techniques can be used to determine the free chloride ion c o n t e n t of s p e c i m e n s c o n t a i n i n g e x t e r n a l l y d e r i v e d chloride, but that less severe extraction conditions are necessary. It is o u r e x p e r i e n c e t h a t a f t e r g r i n d i n g , c e m e n t p a s t e of any age will continue to h y d r a t e if i m m e r s e d in water. For the m i x e s t e s t e d the c h a n g e s in pore s o l u t i o n c o m p o s i t i o n w e r e s u f f i c i e n t l y small b e y o n d 28 d a y s for us to a c c e p t t h i s as a r e a s o n a b l e p e r i o d of curing. The aim of the work on p a r t i c l e size was to d e t e r m i n e the i n f l u e n c e of f i n e n e s s on the q u a n t i t y of c h l o r i d e p a s s i n g into solution for a practical period of leaching. The effect of l e a c h i n g t i m e was s t u d i e d s e p a r a t e l y (see f i g u r e s 4-6). E t h a n o l was i n c l u d e d as an a l t e r n a t i v e s o l v e n t to w a t e r in our s t u d y b e c a u s e o t h e r w o r k e r s [1,2] had p r e v i o u s l y a s s u m e d that the c h l o r i d e s l e a c h e d into e t h a n o l g i v e a g o o d a p p r o x i m a t i o n of the free chloride ion content; in one case, drawing important c o n c l u s i o n s r e g a r d i n g the s t a t e of c h l o r i d e in c o n c r e t e b a s e d on this assumption. Our theoretical work suggested that this a s s u m p t i o n c o u l d well be i n c o r r e c t and we felt it w o r t h w h i l e to investigate this experimentally. We have not studied the chemical c o n s t i t u e n t s of h a r d e n e d c e m e n t p a s t e 664
interaction and m e t h a n o l
between and, in
the view
Vol. 18, No. 4
665 OISCUSSIONS
of the p o o r p e r f o r m a n c e of m e t h a n o l as a l e a c h i n g agent, it is not our i n t e n t i o n to do so. H o w e v e r , our u n d e r s t a n d i n g of the l i t e r a t u r e [3] is t h a t it is by no m e a n s an e s t a b l i s h e d fact that methanol reacts with cement paste constituents. References i. V.S. R a m a c h a n d r a n , M a t e r i a u x et Constr., 14, 3 (1971). 2. N. Tenoutasse, "A simple method for the determination of calcium chloride during cement hydration", International Symposium on A d m i x t u r e s in m o r t a r s and c o n c r e t e , Brussels, R I L E M - A B E M , R e p o r t V / 1 5 V, 261 (1967). 3. L.J. Parrot, Cem. Concr. Res., 13, 65 (1983).